The essential growth structures of hair are the so-called hair follicles which are present in the skin. These hair follicles produce hair follicle cells or keratinocytes. During their journey to the surface of the skin the cytoplasm of these cells is converted by a large number of complex processes into the tough and elastic material which is known as hair. The growth cycle of hair can be subdivided into three phases: the anagen phase (‘growth phase’), the catagen phase (‘transitional phase’) and the telogen phase (‘death phase’). The hair follicle is unique in the cyclic nature of hair formation and hair growth. It is the only part of the body that has a growth nucleus, from which new hairs can be produced after removal of the old hair.
Human beings usually find baldness undesirable from a cosmetic and aesthetic point of view. Baldness occurs frequently, however, and it is a known phenomenon that men in particular become balder as they get older. It does also occur in women, however, and is then in particular highly undesirable from a cosmetic and aesthetic point of view.
A known technique for combating baldness is the transplantation of hair. With this procedure hair, including the skin, is removed from a donor area covered with hair which is often located on the back of the head, and is cut into small pieces which usually only contain one to three hairs. These pieces are then implanted in the bald area (receptor area). A significant disadvantage of this technique is that this is at the expense of the donor area. After all, hair is removed from this area and this hair does not grow back. This transplantation technique therefore offers limited possibilities.
It is known that hair follicle cells can be cultured from plucked human hair. It is also known that it is difficult to form a differentiated epidermis or a completely developed epidermis with the aid of such cultured cells, both in vitro and in vivo. Cultured hair follicle cells from mice can stimulate hair growth when they are implanted in test animals.
A method for the reproduction of hair in human beings is described in European patent application 0 236 014, in which epidermal follicle cells of the desired hair type are removed from the head hair of a patient. The epidermal follicle cells are then cultured in a culture medium which preferably contains growth factors. An opening is then made in the epidermis of the patient's scalp and the cultured epidermal follicle cells are introduced via this opening into the dermis next to the epidermis. The disadvantage of this method is that it includes an invasive method and that the cells are not placed in a targeted manner, so that many cells are needed and the probability of the regeneration of hair is less.
Another method for the reproduction of hair is described in European patent application 0 971 679. Here the hair is removed from a donor area in such a way that new hairs come back in place thereof, while new hair follicle cells are cultured from the hairs removed, from which cells can once again form new hair. Renewed hair growth can thus be achieved without this being at the expense of the donor area. To this end hair follicle cells removed in the anagen phase are cultured for 1 hour to 40 days in a serum-free keratinocyte culture medium. A disadvantage of this method is the long time that is needed for culturing the hair follicle cells.